60 



slightly on the left and the other broadly on the right and is 

 followed by a longitudinal series of six or seven plates as dis- 

 closed between the arms, and, on the right of this series, and 

 separated from it by a nearly straight suture, there is a longi- 

 tudinal series of seven plates; on the left and separated by a 

 longitudinal suture there are nine plates in a double series, 

 arranged w T ith some irregularity. There are, therefore, as many 

 as twenty-live or twenty-six plates in this area. It will be seen 

 that if the distinction between Taxocrinus and Forbesocrinus is 

 dependent upon the azygons area that we have here a Tn.ro 

 crimes by reason of the longitudinal series of plates, and a 

 Forbesocrinus by reason of the large area. 



This species will be readily distinguished by its quinquelobate 

 form, number of primary and secondary radials and shape of 

 the interradial areas and by the azygous plates. 



Found by the late Wm. McAdams, in whose honor the speci- 

 fic name is given, in the Keokuk Group, in Jersey county, Illi- 

 nois, and now in the collection of Wm. P. E. Gurley. 



Family PLATYCRINID^. 



PLATYCRINUS FORMOSUS, var., APPROXIMATUS, 11. var. 



PZa/e IV, Fig. 8, basal view; Fig. 9, summit view; Fig. 10, 

 azygons side view; Fig. 11, opposite side. 



This species or variety is medium size and belongs to the 

 discoid forms. It is so much like P. formosus that it can only 

 be called a variety, in the absence of a knowledge of the vault 

 of that species, and, if the vaults are alike then the varietal 

 name may be stricken out. but if the vaults are differently 

 constructed then the varietal name may have the rank of a 

 species. The calyx is shallow, though deeper than in the 

 types of P. formosus, pentagonal, three times as wide as high. 

 Plates thick and bearing low rounded nodes less conspicuous 

 than they are in the types of P. formosus. Sutures beveled but 

 net canaliculate as they are in P. formosus. 



Basals form a concave pentagonal disc bordered by a nodose 

 rim. The first radials are rounded upward from the basal 

 suture and constricted in the middle part, beyond which they 

 are directed horizontally, and the facet for the second plate is 



